In copy trading, you allocate a portion of your account to "follow" another trader. When they open a trade, your account opens the same trade proportionally; when they close, you close. Popular platforms include eToro's CopyTrader, ZuluTrade, and MT4/MT5 signal services.
Copy trading is not passive income — it is still trading, and most copied traders lose money over long periods even if they have strong recent results. The best practical approach is to diversify across several copied traders with different styles, cap the percentage allocated to any single trader, and treat the whole allocation as higher-risk than a self-managed portfolio.